The present invention belongs to a technical field of a pretensioner provided in a seatbelt retractor for retracting a seatbelt and using a plurality of force transmission members formed by balls, a technical field of a seatbelt retractor, and a technical field of a vehicle seatbelt apparatus.
For seatbelt apparatuses to be mounted in vehicles such as automobiles, a variety of seatbelt retractors including a pretensioner have been developed. At the beginning of an emergency, such as a vehicle collision, in which a deceleration higher than the normal deceleration is applied to a vehicle, a pretensioner rotates a spool of a seatbelt retractor in a seatbelt retracting direction by using reactant gas generated in a gas generator, thereby retracting a seatbelt on the spool. This quickly takes up slack in the seatbelt and applies tension to the seatbelt so as to increase the occupant restraint force.
As an example of a pretensioner of the related art, a pretensioner is known in which a plurality of force transmission members formed by balls are stored in a pipe, these force transmission members are moved along the interior of the pipe by force of reactant gas generated by a gas generator in case of an emergency so as to press a plurality of pressed portions of a ring gear formed by levers, so that the ring gear is rotated to rotate a spool in a seatbelt retracting direction (for example, see PTL 1, WO/2010/084687, which is incorporated by reference herein).
In the pretensioner described in PTL 1, to be pressed by the plurality of force transmission members formed by balls, the plurality of pressed portions of the ring gear need to enter a moving path of the force transmission members in the pipe. For this reason, as illustrated in FIG. 8, a narrow and long cutout portion 102 extending in a longitudinal direction of a pipe 101 is provided in the pipe 101, and pressed portions 104 of a ring gear 103 enter a moving path of force transmission members 105 in the pipe 101 through the cutout portion 102. In this type of pretensioner, the outer diameter of the force transmission members is set to be smaller than the inner diameter of the pipe 101 so that the force transmission members can move smoothly.